1. Field of the Invention
The present invention relates to a structure and a method for connecting a coated lead wire with a land portion, and a clad material adapted for lead wire connection.
2. Description of the Related Art
In JP-A-9-84191, a process of removing an insulating coating of a conductor wire is carried out independently of a process of connecting the wire with an electrically conductive adhesive agent. In JP-A-9-84192, a process of removing an insulating coating of a conductor wire is carried out independently of soldering. In JP-A-9-200895, a land portion to which a coil terminal is to be connected has a substantially circular shape to prevent occurrence of a defect in connection due to a solder splitting phenomenon.
In soldering connection, the improvements as described above are needed to prevent occurrence of a defect in connection. As a result, the shape of the land portion is restricted. Especially, a coil terminal connectable region is limited in a very small component such as an electroacoustic transducer. Accordingly, the restriction of the shape of the land portion results in that the degree of freedom in product design is limited.
As a recent measure against environmental problems, it is desired that elements which may have a possibility to give a bad influence to an environment are refrained from being used to the utmost in production of electronic components, circuit boards, electronic equipment, and the like. Especially, soldering is a popular method for electrically connecting conductors. If electronic equipment is illegally dumped, lead contained in solder might be eluted and adversely affect the environment.
It is considered to use lead free soldering as a measure against the environment problems. However, such a lead-free soldering has a higher melting point in temperature than any one of the methods in the conventional art. Accordingly, the component material must be high in heat-resistance and the producing cost thereof increases.
An object of the present invention is to provide a structure and a method of lead wire connection in which electric connection can be performed surely between conductors without using any solder, and to provide a clad material adapted for lead wire connection.
According to an aspect of the present invention, there is provided a structure of lead wire connection comprising:
a lead wire covered with an electrical insulating coating;
a land portion electrically connected to the lead wire; and
a cover member disposed in opposition to the land portion with the lead wire held between the land portion and the cover member;
wherein the cover member and the lead wire are electrically connected by resistance welding; and
the lead wire and the land portion are also electrically connected by resistance welding.
According to the present invention, since resistance welding is carried out in a condition that the cover member is disposed on the lead wire, an electrode tool for resistance welding does not come into direct contact with the lead wire. Accordingly, it is possible to prevent damage or disconnection of the lead wire from occurring. Even if the lead wire is extra fine, electrical connection can be carried out surely.
Further, since the cover member is interposed between the lead wire and the electrode tool, the pressing force of the electrode tool can be set to a high value so that the contact area between the cover member and the lead wire and the contact area between the lead wire and the land portion increase. As a result, the welding area becomes large and reduction in the connection resistance can be attained.
Further, conductors can be electrically connected surely to each other without using any solder. Accordingly, a bad influence on the environment due to the elements composing the solder can be eliminated.
Further, a liquid binder such as solder becomes unnecessary. Accordingly, regardless the shape of the land portion, no defect in connection due to a solder splitting phenomenon is generated. As a result, the degree of freedom in design of shape of the land portion is improved greatly.
Further, according to the present invention, there is provided a method of lead wire connection comprising:
mounting a lead wire covered with an electrical insulating coating onto an upper surface of a land portion;
supplying a cover member onto the lead wire;
pressing the lead wire via the cover member against the upper surface of the land portion by a first electrode tool having a heater mechanism while supporting a lower surface of the land portion by a second electrode tool;
heating the first electrode tool by the heater mechanism to make the lead wire exposed partially; and
applying an electric current between the first and second electrode tools so that resistance welding is effected between the cover member and the lead wire and between the lead wire and the land portion.
According to the present invention, if the heater mechanism is operated in a condition that the cover member, the lead wire, and the land portion are held between the first and second electrode tools, the coating of the lead wire is partially removed by heat to thereby make the lead wire exposed. In this condition, the electric contact of the first electrode tool with the cover member, the lead wire, and land portion is attained. Next, when an current is applied between the first and second electrode tools, much Joule heat is generated in a contact portion where the electric resistance is high so that the cover member and the lead wire are subjected to resistance welding, and the lead wire and the land portion are also subjected to resistance welding.
Since resistance welding is performed in a condition that the cover member is disposed on the lead wire, the electrode tool for resistance welding does not come into direct contact with the lead wire so that the lead wire can be prevented from being damaged or disconnected. Accordingly, even if the lead wire is extra fine, it is possible to realize the electric connection surely.
Further, since the cover member is interposed between the lead wire and the electrode tool, the pressing force of the electrode tool can be set to a high value so that the contact area between the cover member and the lead wire and the contact area between the lead wire and the land portion increase. As a result, the welding area becomes large and reduction in the connection resistance can be attained.
Further, conductors can be electrically connected surely to each other without using any solder. Accordingly, a bad influence on the environment due to the elements composing the solder can be eliminated. Further, a defect in connection due to a solder splitting phenomenon can be eliminated so that the degree of freedom in design of shape of the land portion is improved greatly.
Further, according to the present invention, there is provided a method of lead wire connection comprising:
mounting a lead wire covered with an electrical insulating coating onto an upper surface of a land portion;
supplying a cover member onto the lead wire;
pressing the lead wire via the cover member against the upper surface of the land portion by a pressure welding tool having a heater mechanism; and
heating the pressure welding tool by the heater mechanism to make the lead wire exposed partially, and to supply a melted portion of the cover member around the lead wire and the land portion.
According to the present invention, when the heater mechanism is operated in a condition that the cover member, the lead wire, and the land portion are pressed by the pressure welding tool, the coating of the lead wire is partially removed by heat to thereby make the lead wire exposed. In this condition, as the temperature of the pressure welding tool becomes high, the cover member is partially melted and the melted material is supplied to the connection portion between the lead wire and the land portion.
Since thermal welding is performed in a condition that the cover member is disposed on the lead wire, the pressure welding tool does not come into direct contact with the lead wire so that the lead wire can be prevented from being damaged or disconnected. Accordingly, even if the lead wire is extra fine, it is possible to realize the electric connection surely.
Further, since the cover member is interposed between the lead wire and the pressure welding tool, the pressing force of the pressure welding tool can be set to a high value so that the contact area between the cover member and the lead wire and the contact area between the lead wire and the land portion increase. As a result, the welding area becomes large and reduction in the connection resistance can be attained.
Further, conductors can be electrically connected surely to each other without using any solder. Accordingly, a bad influence on the environment due to the elements composing the solder can be eliminated. Further, a defect in connection due to a solder splitting phenomenon can be eliminated so that the degree of freedom in design of shape of the land portion is improved greatly.
Further, according to a still further aspect of the present invention, the cover member includes a laminate of a plurality of metal materials having different melting points in which the metal material brought into contact with the lead wire has a melting point lower than a melting point of the metal material brought into contact with the pressure welding tool.
According to the present invention, since a material of a high melting point is disposed on the pressure welding tool side and a material of a low melting point is disposed on the lead wire side, the low melting point material is melted first upon welding and supplied to the connection portion between the lead wire and the land portion. Therefore, the melted material of the cover member plays roles of reinforcing the connection strength, reducing the connection resistance, performing oxidation protection, and so on. On the other hand, since the high melting point material is not melted, separation of the cover member from the pressure welding tool is easy so that the pressure welding tool can be prevented from contamination.
Further, according to the present invention, there is provided a clad material for lead wire connection comprising:
a laminate of a plurality of metal materials having different melting points,
wherein the clad material is disposed between a lead wire and a welding tool when the lead wire and a land portion are connected by resistance welding or thermal welding.
According to the present invention, when a clad material constituted by a laminate of a high melting point material disposed on the welding tool side and a low melting point material disposed on the lead wire side is used as the cover member, the low melting point material is melted first upon resistance welding or thermal welding and supplied to the connection portion between the lead wire and the land portion. Therefore, the clad material plays roles of reinforcing the connection strength, reducing the connection resistance, performing oxidation protection, and so on. On the other hand, since the high melting point material is not melted, separation of the cover member from the welding tool is easy so that the welding tool can be prevented from contamination.